Osteopenia

Osteopenia is a lower-than-normal bone density. The condition occurs when bone cells are reabsorbed by the body more quickly than the body can make new bone. However, having osteopenia does not necessarily indicate that bone loss is occurring because some people have naturally lower bone density. The bone density in osteopenia is not low enough to be considered osteoporosis, but can be a risk factor for developing osteoporosis.

The prevalence of osteopenia in the United States among adult males and females aged 50 and older is 28%–47% and 30%–50%, respectively, including non-Hispanic Caucasians, non-Hispanic African Americans, and Mexican Americans. Differences in bone density between the three racial groups are not significant, except for a greater prevalence of osteopenia among Mexican American women compared to non-Hispanic Caucasian and African American women.

Age and gender are both associated with increased incidence and prevalence of osteopenia. All individuals, male and female, lose bone density as they age, starting at about age 30, when peak bone density is reached. More women develop osteopenia than men because they have a lower peak bone density, and the loss of bone mass accelerates when estrogen levels are reduced during menopause. Osteopenia is found less frequently in individuals who engage in bone-loading exercise, which helps to protect or actually increase bone density; it is found more frequently in those who participate in non-weight-bearing sports, such as bicycling or swimming, especially in young female athletes with lower body weight and lower fat levels. In middle-aged men, a higher prevalence of low bone mass is associated with the presence of metabolic syndrome, a cluster of symptoms including increased waist circumference (abdominal fat), elevated cholesterol levels, high blood pressure, and high blood glucose (prediabetes).

Osteopenia is not a disease in itself but may be a precursor to osteoporosis in individuals at higher risk. Because osteopenic bone density is lower than the normal peak bone density in adults, having osteopenia may mean that an individual has a greater risk of further bone loss and developing the weak and brittle bones of osteoporosis. Beginning in middle age, the body cannot keep up with creating new bone as existing bone cells are reabsorbed by the body. Consequently, the bones lose minerals, heaviness (bone mass), and structure (bone density). Having stronger and thicker bones at about age 30 will slow the process of developing osteopenia that typically occurs with aging. Also, those who do develop osteopenia may not develop osteoporosis. Some individuals simply have a lower natural peak bone density, whereas others with certain genetic and lifestyle factors are at higher risk for osteoporosis and spontaneous bone fractures as they age.

Many physical, genetic, and lifestyle factors may increase the risk of developing osteopenia, including:

Osteopenia has no noticeable symptoms, such as pain. However, individuals with progressive osteopenia may have increased risk of spontaneous bone fracture; because osteopenia is without symptoms, sometimes a spontaneous fracture without trauma is the first sign of a loss of bone density.

Osteopenia is diagnosed primarily by dual-energy x-ray absorptiometry (DEXA), a sensitive form of x-ray that is able to detect losses of bone mass as small as 3%. Standard x-ray images are not helpful in diagnosing osteopenia; however, portable ultrasound imaging and portable x-ray machines can measure bone density in the heel. DEXA is used to evaluate bone density in the spine, total hip, and the femur neck; grades called T-scores are assigned to designate specific levels of bone loss. Physicians often assess risk in osteopenic patients using a fracture-risk calculator such as FRAX, developed by the World Health Organization, rather than relying on T-scores alone.

The Unites States Preventive Services Task Force has recommended that all women age 65 and older have bone density tests to screen for osteopenia and osteoporosis, and anyone at increased risk of losing bone mass should be screened regularly after age 30.

The goal of osteopenia treatment is to keep it from progressing to the more damaging osteoporosis, and adopting a healthy lifestyle is the mainstay of treatment. Level of fracture risk, which must be determined for each person, indicates whether or not treatment is needed. Nevertheless, one of the most important lifestyle measures to protect against developing osteoporosis is to increase physical activity because the body responds to muscle stress from physical exercise by manufacturing bone tissue. For those who wish to increase exercise without participating in any recreational sports, many fitness clubs and gyms have programs with a range of activities at different levels of intensity, including strength training to increase muscle elasticity and strengthen connective tissues, tendons, and ligaments. Such training helps to maintain a healthy bone mass and prevent age-related losses of bone and muscle. Individuals who are not participating in a fitness program are urged to increase weight-bearing exercises such as walking, hiking, and dancing. Yoga, whether gentle or vigorous, uses all muscle groups in the body and is noted for improving overall health status and mobility in individuals of any age.

It is especially important for the physician to determine whether individuals with osteopenia need treatment or not. Medications may be recommended for some individuals with osteopenia who have a family history of osteoporosis or have several risk factors for osteoporosis. A group of biphosphonate drugs, including alendronate (trade name Fosamax), ibandronat (trade name Boniva), and risedronate (trade names Actone, Atelvia) are bone-friendly prescription medications designed to slow bone loss in individuals with osteopenia and risk factors for osteoporosis. Drugs classified as selective estrogen receptor modulators (SERMs) may also be prescribed for women with osteopenia, although study results have shown that benefits in protecting against osteoporosis are fewer than expected.

The prognosis for osteopenia is good to excellent in otherwise healthy individuals who exercise regularly, eat a bone-healthy diet, and avoid lifestyle factors such as smoking and drinking alcohol. Individuals with osteopenia and risk factors for osteoporosis can delay progression of osteoporosis or prevent it by correcting deficits in physical exercise and diet, making appropriate lifestyle changes such as stopping smoking and alcohol consumption, and avoiding medications known to increase risk for osteoporosis and fractures.

Osteopenia is not inevitable event, though adult men and women do begin losing bone mass as early as age 30. Maintaining bone health is the key to avoiding or preventing progressive osteopenia and possibly osteoporosis later in life. Weight-bearing exercise and regular physical activity are known to boost bone health. The best time to improve bone mass through exercise is during childhood and adolescence, setting a course for regular exercise and sports activity, which is shown to reduce risk for osteoporosis and fractures in older adults. Studies of postmenopausal women, who are believed to be at greater risk of osteoporosis, have shown that bone mineral density can be maintained or even increased with sufficient therapeutic exercise. For older adults who do not participate in competitive sports or recreational exercise, even nonstrenuous but weight-bearing tai chi, when performed regularly, has been shown to improve balance and bone density, reducing the incidence of falls by as much as 47% and hip fracture by 25%

Calcium, like exercise, is necessary for healthy bones. To maintain bone health, the amount of calcium circulating in the body must stay within a very narrow range. Bone acts like a calcium bank, storing calcium to replace any shortage in circulating calcium when needed. Bone is constantly being broken down by cells called osteoclasts and built up again by cells called osteoblasts. This process is called bone remodeling, and it continues throughout an individual's life. When excess calcium is present in the blood, osteoblasts deposit calcium into bones. When too little calcium is in the blood, osteoblasts dissolve calcium from bones and move it into the blood. This process is controlled by parathyroid hormone (PTH) secreted by the parathyroid glands. The parathyroid glands are extremely sensitive to calcium levels in the blood, and in healthy individuals they are able to maintain the concentration of calcium ions so it fluctuates very little.

L. Lee Culvert